1. Field of the Invention
The present invention relates generally to a wireless communication system, and more particularly to a communication method for improving the flexibility of resource allocation and maximizing the system performance through an enhanced hybrid duplexing technology (EHDT) that selectively applies diverse duplexing modes.
2. Description of the Related Art
The next-generation wireless communication system, including the 3rd generation mobile communications, attempts simultaneous support of multimedia services of diverse traffic characteristics such as broadcastings and real-time video conferences in addition to voice services. Accordingly, in order to efficiently provide services of such diverse characteristics, a duplexing technique in consideration of asymmetry and continuity of uplink/downlink according to the service characteristics is required.
Generally, the duplexing technique is classified into a time division duplexing (TDD) and a frequency division duplexing (FDD). TDD is a technique for implementing bidirectional communication by dividing the same frequency band into time slots and alternately switching transmission and reception slots. An FDD is a technique for implementing bidirectional communication by dividing a given frequency band into transmission and reception bands.
In a TDD-based communication system, a base station can allocate a part or all of usable time slots to a terminal, and through this variable allocation of the time slots, asymmetric communication is possible. However, in TDD, if the radius of a cell is extended, a protection section between the transmission/reception time slots is increased due to a round trip delay and this causes the transmission efficiency to be lowered. Accordingly, it is improper to use TDD in a communication environment in which the cell has a large radius such as a macro cell.
Additionally, in TDD, the asymmetric ratios of the respective cells are not equal to each other in a multi-cell environment, and thus severe frequency interference occurs between terminals located on the border of an adjacent cell.
In an FDD-based communication system, the frequency bands for transmission and reception are separated from each other, and thus no time delay for the transmission or reception occurs. Accordingly, no round trip delay due to the time delay occurs. Therefore, FDD is suitable to the cell environment in which the cell has a large radius such as the macro cell.
However, in FDD, the transmission frequency band and the reception frequency band are fixed, which it is not proper for duplexing the asymmetric transmission.
Therefore, research into duplexing techniques that mix the two kinds of duplexing techniques in consideration of the diverse next-generation communication environments and traffic characteristics is being actively progressed.
FIG. 1 illustrates a conventional duplexing technique based on a dual band. Referring to FIG. 1, a base station performs the same-period transmission/reception mode conversion with respect to two frequency band channels, i.e., wide-band and narrow-band channels, and terminals connected to the base station operate in a reverse mode to the base station and are allocated with resources for reception and transmission on the two frequency band channels without any overlap. That is, with respect to the wide-band channel 101a of the transmission mode section of the base station, terminal #1 and terminal #2 each occupy half of the wide-band channel 101a as their reception mode sections, and terminal #3 and terminal #4 are allocated with parts of the narrow-band channel 103A of the base station transmission mode section as their reception mode sections 103A-2 and 103A-1, respectively. Additionally, with respect to the wide-band channel 101b of the reception mode section of the base station, terminal #1 and terminal #4 occupy parts of the wide-band channel 101b as their transmission mode sections 101b-1 and 101b-2, and terminal #2 and terminal #3 occupy parts of the narrow-band channel 103B of the base station reception mode section as their transmission mode sections 103B-2 and 103B-1, respectively.
Although the duplexing technique based on the dual band as described above enables flexible resource allocation possible by combining and allocating the wide-band channel and the narrow-band channel, it is difficult to expect the link continuity inherent in FDD because the transmission/reception mode conversions of the wide-band channel and the narrow-band channel are simultaneously performed.
FIG. 2 illustrates a duplexing technique based on band switching. According to this duplexing technique based on a band switching, an uplink and a downlink are periodically repeated for a specified period (Tsec) within one band, and thus the other band is simultaneously used as the uplink and downlink with the channel conversion characteristic of TDD. However, when duplexing based on the band switching, because the same band channels are used, the flexibility of resource allocation is lowered and it is difficult to implement an asymmetric transmission by the periodic channel conversion.